Roof joist for modular building and methods

ABSTRACT

A roof joist for a roof section of a modular building having an interior ceiling with a length, having an upper chord, central chord, and lower chord. The lower chord comprises: (i) a top chord segment joined to, and parallel with, the central chord; (ii) a pair of sidewall chord segments that oppose one another and extend parallel to the top chord segment; and (iii) a pair of outer flanges that extend outwardly from the sidewall chord segments to support the interior ceiling. A pair of inner flanges can also extend inwardly from the sidewall chord segments to support fixtures in the interior of the building.

RELATED APPLICATION

This application claims the benefit of provisional application No.61/060,399 filed Jun. 10, 2008, which is incorporated by referenceherein in its entirety.

BACKGROUND

Embodiments of the present invention relate to a roof joist for amodular building.

Modular buildings are often made from pre-fabricated, portable buildingelements that are designed to facilitate shipment and assembly of abuilding structure at a building site. Modular buildings can also betransported in large preassembled sections and then connected at thebuilding site. Such buildings reduce fabrication and assembly costs byallowing mass production and partial assembly of common parts andsections of buildings. They can also be rapidly deployed to replacedamaged buildings after natural disasters, such as hurricanes andearthquakes. As such, modular building structures have unique designrequirements which are different from conventional buildings. Forexample, modular buildings can be designed to allow flexibleconfigurations for different types of external configurations andinterior spaces. They can also be designed facilitate ease of assemblyonsite and at a building location. Further, when used in disaster zones,replacement modular buildings often have to meet strict regionalstandards with respect to seismic resistance and storm-resistantstructural frame.

The structural components and other parts for such modular building alsohave unique requirements. For example, the modular building componentsneed to be designed to facilitate mass production and transport.Component shape standardization can also be used to reduce warehousestorage space required to keep a large number of prefabricatedcomponents. Further, modular parts should also be adaptable to allow fora wide variety of end use applications. In addition, it is desirable fora modular components to be adapted for multiple uses to reduce thenumber of components used in each building.

One component type that needs special attention in such buildingstructures is the roof joist. A roof joist provides load-bearingcapabilities to support the roof structure and resist shearing forces. Anumber of different types of roof joists have been used in buildingconstruction, including, for example, a simple I-beam structure madefrom structural steel. In some embodiments, roof joists are parallelbeams made of timber, steel, or reinforced concrete beams, and areshaped and sized to support the roof of the building. However, many suchembodiments of roof joists are heavy and difficult to transport or evento fabricate. They also have different, non-standardized designs thatare not always readily adaptable to meet the standards of differentbuilding designs.

For reasons including these and other deficiencies, and despite thedevelopment of various roof joist structures and modular buildings,further improvements in roof joists and such buildings are continuouslybeing sought.

SUMMARY

A roof joist can be used in a roof section of a modular buildingcomprising an interior ceiling having a length. The roof joist comprisesan upper chord comprising a length sufficiently long to extendsubstantially across the entire length of the interior ceiling of theroof section of the modular building. A central chord is joined to theupper chord. A lower chord is joined to the central chord. The lowerchord comprises: (i) a top chord segment; (ii) first and second sidewallchord segments that extend downwardly from the top chord segment andoppose one another; and (iii) first and second outer flanges that extendoutwardly from the first and second sidewall chord segments,respectively, the flanges being capable of supporting the interiorceiling.

A method of forming the roof joist comprises: (a) extruding a materialto form an extrusion preform comprising an upper chord, a central chordjoined to the upper chord, and a lower chord joined to the centralchord, the lower chord comprising: (i) a top chord segment; (ii) firstand second sidewall chord segments that extend downwardly from the topchord segment and oppose one another; and (iii) first and second outerflanges that extend outwardly from the first and second sidewall chordsegments, respectively, the flanges being capable of supporting theinterior ceiling; and (b) cutting the extrusion preform when the lengthsof the upper, central and lower chords are each sufficiently long toextend substantially across the entire length of the interior ceiling ofthe roof section of the modular building.

DRAWINGS

These features, aspects, and advantages of the present invention willbecome better understood with regard to the following description,appended claims, and accompanying drawings, which illustrate examples ofthe invention. However, it is to be understood that each of the featurescan be used in the invention in general—not merely in the context of theparticular drawings—and the invention includes any combination of thesefeatures, where:

FIG. 1A is a side sectional view of an exemplary embodiment of a roofjoist for a modular building;

FIG. 1B is a perspective view of the joist of FIG. 1A;

FIG. 2A is a side sectional view of another embodiment of a roof joistfor a modular building;

FIG. 2B is a perspective view of the joist of FIG. 2A;

FIG. 3A is a side sectional view of yet another embodiment of a roofjoist for a modular building;

FIG. 3B is a perspective view of the joist of FIG. 3A;

FIG. 4 is a cross-sectional view of the joist of FIG. 3A showing innerflanges with support tabs for holding a device, and the outer flangesholding ceiling tiles;

FIG. 5 is a cross-sectional view of a roof section of a modular buildingshowing integration of a roof joist into the structure;

FIG. 6 is a side view of a frame of a modular building comprising shedwith tilted roof and side expansion module;

FIG. 7 is a perspective view of a frame of a modular building comprisinga shed, side expansion modules, and a concrete grade beam foundation;and

FIG. 8 is a schematic perspective view of an embodiment of a modularbuilding that uses a plurality of the roof joists to define a roofsection, a ceiling supported by the roof joists, sidewalls, and asupport sled.

DESCRIPTION

An exemplary embodiment of a roof joist 20 for use in a roof section 24of a modular building is shown in FIGS. 1A and 1B. This roof joist 20 ismultifunctional and can be used to both support a roof 26 of a modularbuilding, retain a suspended interior ceiling 28 along the length of theroof section 24, and even support fixtures and other equipment that isused in the interior of the building. In the embodiment shown, the roofjoist 20 comprises an upper chord 30, lower chord 32, and central chord34. Each of the upper and lower chords 30, 32 are end members of theroof joist 20 and span across the entire length of the roof joist 20.The upper and lower chords 30, 32 are substantially parallel to oneanother, and are connected to each other by the central chord 34. Inthis illustrative embodiment, the upper chord 30, lower chord 32, andcentral chord 34 are each depicted as a single longitudinal structure;however, it should be understood that other structures equivalent to thelongitudinal structures, such as a web of structural members (notshown), a plurality of beams (not shown), a honeycomb member (notshown), or other structures apparent to one of ordinary skill in theart, can also be used.

The upper chord 30 has a longitudinal segment 36 with a lengthsufficiently long to extend across substantially across the entirelength of an interior ceiling 28 of the modular building 100. In oneversion, the upper chord 30 comprises a longitudinal segment 36comprising a planar beam 38. The geometry of the planar beam 38facilitates welding or fastening the roof joist 20 in-place to a roofstructure. For example, a set of fasteners 40 comprising screws, nailsor clips can be used to fasten the longitudinal segment 36 to a deckingproduct 71, or to roof panels, roof panel brackets or even drainagechannels.

The central chord 34 is joined to, and parallel with, the upper chord30. In one version, as shown in FIG. 1A, the central chord 34 comprisesa flat beam 46 oriented perpendicularly to the longitudinal segment 36of the upper chord 30.

The lower chord 32 comprises a top chord segment 48 which is also joinedto, and parallel with, the central chord 34. The top chord segment 48can also extend across substantially the entire length of the interiorceiling 28 of the modular building 100. The lower chord 32 furthercomprises a pair of sidewall chord segments 50 a,b that oppose oneanother and extend parallel to the top chord segment 48. In one version,the lower chord 32 forms a U-shaped longitudinal channel 52 with itsopening facing downward. In one version, the U-shaped channel 52 isrectangular, and has a depth of from about 2 to about 4 cm and a widthof from about 4 to about 8 cm.

Each sidewall chord segment 50 a,b of the lower chord 32 supports anouter flange 54 a,b that extends outwardly from the sidewall chordsegments 50 a,b. In one version, the outer flanges 54 a,b extendoutwardly from the lower edge of the sidewall chord segments 50 a,b toserve as outwardly protruding load bearing surfaces. In one example, theouter flanges 54 a,b of the lower chord 32 are used to support aplurality of ceiling panels 76 which form an interior false ceiling 28of the modular building 100 (see also FIG. 4). The false ceiling isuseful for hiding electrical connections, plumbing, ventilation, andother such utilities. The false ceiling 28 can also be used to absorbsound or provide additional insulation. The ceiling panels 76 can bemade from a rigid material that is, for example, thermally insulating,sound absorbing and/or decorative. In one version, the outer flanges 54a,b are sized sufficiently long to support ceiling panels 76 to form aninterior ceiling. In this example, each outer flange 54 a,b has a lengthof from about 2 to about 4 cm, extended to an adequate length to supportthe ceiling panels 76. The outwardly extending flange 54 a,b is alsoseparated from the roof 26 of the structure by a distance of from about12 to about 18 cm. This separation provides acoustic and thermalinsulation between the interior and the exterior of the structure whenthe pair of outer flanges 54 a,b are used to support the false ceiling.

The sidewalls of the lower chord 32 can also have inner flanges 58 a,bthat extend inwardly from the sidewall cord segments 50 a,b. The pair ofinner flanges 58 a,b serve as support members to support fixtures 59,such as equipment and objects used in the interior of the building. Forexample, the inner flanges 58 a,b can be used to support fixtures 59such as for example windows, sidewall panels, screens or even doors. Inone version, the inner flanges 58 a,b extend inward from the sidewallsby between about ⅛ to about ⅓ of the diameter of the U-shaped channel 52as defined by the lower chord 32. The channel 52 with inner flanges 58a,b can also provide a location for universal attachment of userequipment, such as, for example, lighting, white boards or projectionscreens without the need for drilling, screwing or nailing into thestructure. In one version, each inner flange 58 a,b of the lower chord32 has a length which is sized smaller than a length of each outerflange 54 a,b. In one version, each inner flange 58 a,b comprises alength of from about 1 to about 3 cm, or even about 2 cm. This length issuitable for providing load-bearing support surface for sidewall panelsor other support-tab-equipped fixtures.

In another embodiment, as shown in FIGS. 2A and 2B, the roof joist 20comprises a plurality of longitudinal hollow channels 60 a,b that formseparately enclosed reinforcing structures. In this version, the upperchord 30 comprises a first longitudinal hollow channel 60 a having a boxshape and defining a first enclosed volume 62 a. The central chord 34also comprises two opposing sidewall members 34 a,b that are parallel toone another and join the upper chord 30 and the lower chord 32 to alsoform a second longitudinal hollow channel 60 b, which has a box shapeand defines a second enclosed volume 62 b. The top chord segment 48forms a common wall between the lower chord 32 and the central chord 34.

The first and second longitudinal hollow channels 60 a,b serve asreinforcing structural members that allow the roof joist 20 toaccommodate the structural load of the ceiling with a minimal ofstructural material and weight. This structure decreases the weight ofeach roof joist 20 and the lower weight also facilitates transportationof the joists. The hollow longitudinal channels 60 a,b also have dualfunction in that, in addition to serving as a support for roof andceiling panels, they also provide an enclosed hollow leakage-containingstructure to retain moisture seepage from the ceiling or sidewallswithout allowing permeation of this moisture into the building. Forexample, fasteners such as screws or clips can be attached into or eventhrough the longitudinal segment of the joist 20 without risk of leakageinto the building. The sidewalls of the second hollow channel 60 b canbe drilled and fastened to provide support points for wires orelectrical connections, plumbing, ventilation or other utilities whilesubstantially reducing risk of moisture seepage from the first hollowchannel 60 a.

In one version, the second enclosed volume 62 b is sized larger than thefirst enclosed volume 62 a. For example, the second enclosed volume canbe at least 1.5 times larger than the first enclosed volume. A ratio of1.5 provides a reduced region for external water containment which cansubject the beam to a greater structural load. In addition, the ratio ofthe first and second volumes serves to provide a selectively largerregion for the fastening of internal or external components to the joist20. For example, increasing the volume ratio from 3:2 to a volume ratioof 4:1 allows a greater surface area for drilling and fastening ofinterior components to the joist 20.

In still another version, as shown in FIGS. 3A and 3B, the roof joist 20comprises a single longitudinal hollow channel 60 that forms an enclosedreinforcing structure. In this version, joist 20 comprises an upperchord 30 comprising a planar beam 38, and a lower chord 32 comprising atop chord segment 48. The top chord segment 48 of the lower chord 32 isjoined to the planar beam 38 of the upper chord 30 by a plurality ofcentral chords, such as the pair of flat beams 46 a,b. The flat beams 46a,b are oriented perpendicular to the longitudinal segment 36 of theupper chord 30. The hollow channel 60 is bounded by the top chordsegment 48, the flat beams 46 a,b and the planar beam 38. The hollowchannel 60 can serve as a reinforcing structural member and can evenprovide an enclosed hollow leakage-containing structure if an exteriorwall of the channel 60 is punctured. For example, if the planar beam 38is drilled and fastened with roof tiles or roof tile support brackets,the hollow channel 60 receives seepage from the roof and preventspermeation of this moisture into the building.

The inner flanges 58 a,b can have a shaped surface to reduce accidentalslippage of load-bearing support tab 78. In one version, each of theinner flanges 58 a,b are equipped with an inner ridge 82 a,b,respectively. In this version, the inner ridges 82 a,b can, for example,extend upward from the load-bearing surface by a distance of from about0.1 to about 0.5 cm. As shown, the inner ridges 82 a,b can have across-sectional profile that is triangular (as shown in FIG. 3A) orcircular or U-shaped (as shown in FIG. 4). A triangular cross-sectionalprofile can allow the inner ridges 82 a,b to contact the downward facingsurface of support tab 78 over a reduced area and form an indentation inthe support tab 78 when the tab is made of a material that is moreductile than the lower chord material and is subjected to load.

Alternatively, the load-bearing upper surface of each inner flange 58a,b and the downwardly facing surface of the support tab 78 can beshaped to mate together as shown in FIG. 4. For example, the support tab78 can comprise a rotatable brad having grooves 80 a,b to correspondwith the ridges 82 a,b. When the support tab 78 is installed in theU-shaped channel 52, the grooves 80 a,b of the support tab 78 mate withthe ridges 82 a,b of the inner flanges 58 a,b. The support tab 78 havinggrooves 80 a,b that correspond with the ridges 82 a,b of the U-shapedchannel 52 is harder to rotate under load and has a reduced chance ofslippage from the U-shaped channel 52.

The roof joist 20 can be fabricated by a number of different methods. Inone version, the roof joists 20 comprise a shaped extruded structurewhich has a consistent cross-sectional shape throughout its length. Inthis method, the roof joist 20 is formed by extruding a material to forman extrusion preform comprising upper chord 30, a central chord 34joined to the upper chord 30, and a lower chord 32 joined to the centralchord 34, the lower chord 32 comprising: (i) a top chord segment; (ii)first and second sidewall chord segments 50 a,b that extend downwardlyfrom the top chord segment 48 and oppose one another; and (iii) firstand second outer flanges 54 a,b that extend outwardly from the first andsecond sidewall chord segments 50 a,b, respectively, the flanges beingcapable of supporting the interior ceiling 28. The extrusion preform iscut when the length of the upper, central and lower chords 30, 34, 32are each sufficiently long to extend substantially across the entirelength of the interior ceiling 28 of the roof section 24 of the modularbuilding 100. However, it should be noted that the roof joist 20 canalso be made by other non-extrusion methods, for example: cutting andwelding of metal tube and sheet stock, bending and welding of multipleformed parts, and pultrusion, as would be apparent to those of ordinaryskill in the art.

The roof joist 20 can be made from a metal, including steel, aluminum,iron, tin, or alloys thereof. The roof joist 20 can also be made from apolymer or composite material. In one example, the roof joist 20 is madefrom extruded aluminum which is lightweight, strong and relativelyflexible. The roof joist 20 can also be made from a reinforced compositematerial, such as carbon or polyimide fibers in an epoxy matrix.

The roof joist 20 can be used in any building, including a modularbuilding 100 that is rapidly deployable, easily transportable, and whichis designed to minimize on-site assembly, as shown in FIGS. 5 to 7. Insuch a building, a plurality of spaced-apart roof joists 20 form trussesthat support the roof 26 by spanning the width between the ceilingbeams. The roof joist 20 comprises features that allow for theattachment of trim pieces that can protect the modular building 100 fromthe elements and even add to the building's modern design aesthetic.Said mounting features can be manifested in a variety of forms, such asa plate that is welded to the end of the joists with holes for screwattachment, attachment features that are continuously extruded through aroof joist profile, or a clip attachment that is screwed or welded tothe roof joists (not shown). The roof joist 20 can also be used to spanfrom the ceiling beams to the headers of outer walls. Further, roofjoists 20 a which are positioned at the outer edge of the ceiling canhave outer flanges 54 a,b which allow for the attachment of externallylocated roof drainage channels 74 (as shown in FIG. 5), plumbing, oreven electrical conduits.

The roof joist 20 supports a roof 26 which can be a variety of differentstructures. For example, a decking product 71 can be attached to the topof a roof joist 20 to form a rigid surface that supports a roof section24, as shown in FIG. 1A. For example, the decking product 71 can be acorrugated, screw-fastened or welded decking product. The deckingproduct 71 can be fastened to the roof joist 20 to form a continuousrigid surface. The roof material can be, for example, insulation or roofmembrane materials.

Alternately, the roof 26 can comprise roof panels 70 that are fasteneddirectly to the longitudinal segments 36 of the roof joists 20 or thatare fastened to the joists 20 through intermediary roof panel brackets72. An embodiment of a roof structure having intermediary roof panelbrackets 72 and roof panels 70 is shown in FIG. 5. The roof panel 70shown comprises a shaped panel with attachment flanges and arcuate topsurface. The ends of the roof panel 70 slope downward towards a drainagechannel 74 that is mounted on an end roof joist 20 a. The roof panel 70can even be an interlocking panel that is equipped with grooves tosnap-fit or otherwise interlock with other roof panels 70 to form acontinuous rigid roof structure.

The roof joists 20 and roof 26 are used to cover the structural frame ofa modular building 100 as shown in FIGS. 6 and 7. The modular building100 comprises a sled 102 supporting a shed 104 with side expansionmodules 106. The sled 102 comprises a rectangular frame composed ofwide-flange beams 126 that are spaced apart and rest on underlying anconcrete grade beams 124. The wide-flange beams 126 are oriented in arectangular configuration and are joined to one another by high-strengthbolts 128. The sled 102 can be anchored into the concrete grade beams124 and leveled using cast-in-place or post-poured, drilled, highstrength bolts. The wide-flange beams 126 can even be equipped withcustom mounting surface such as welded flat plates 130 that enable themto be mounted to the concrete grade beams 124. The concrete grade beams124 can be oriented to provide a hollow region underneath the sled 102for placement of prefabricated electrical and ventilation systemcomponents. The constructed sled 102 provides a preassembled structuralplatform with good structural integrity, pre-tested bolted and weldedconnections, and which allows a flexible configuration of any overlyingshed 104.

Floor joists 132 extend across the upper surface of the sled 102 toprovide a floor having structural rigidity and without seams. The floorjoists 132 can comprise conventional tubular sections or beams. A raisedfloor 134 is formed from floor panels 136 placed between the frameworkof the floor joists 132 to provide the necessary structural diaphragmfor the base of the shed 104. As one example, the floor panels 136 canbe made from structural metal decking. As another example, the floorpanels 136 can be composed of concrete-filled metal pans that sit onpedestals so that the underlying cavity can house electrical andmechanical services. The floor panels 136 can also be rearranged to moveoutlets, ports, and air diffusers, providing the user with maximumflexibility. The under-floor distribution of mechanical services for theoverlying shed 104 can include HVAC (heating, ventilation and cooling)tubes, electrical junction boxes and preassembled wiring. Locatingelectrical and mechanical services underneath the floor 134 of the shed104 provides an integrated infrastructure for such services and can betailored without extensive pre-wiring and ventilation planning for theoverlying shed 104.

The shed 104 placed on the sled 102 comprises a steel framework ofspaced-apart columns that are linked to one another by overhead roofjoists 20 and trusses 110, as shown in FIGS. 6 to 7. The joists 20 andtrusses 110 provide a rigid structural roof section 24 with large spansthat has minimal material usage while providing a highly flexible andtailorable interior space. The columns of the shed 104 can include majorcolumns 114 located at the corners of the shed 104 and attached to theoverlying beams of the sled 102 by gussets to provide vertical strengthin support of the ceiling. Minor columns 116 are bolted to the floorjoists 132 of the sled 102. In addition, diagonal columns 118 comprising4×4 structural tubes can also be used to brace the structure of the shed104 and increase its lateral and shear strength. All these tubes arelinked together with tube steel headers 120 and bolted together forgreater strength.

The minor columns 116 can be spaced apart a sufficient distance toaccommodate wall panels, such as light-impermeable panes 186,light-permeable panes 188, such as windows, translucent screens or evendoors. Advantageously positioning the minor columns 116 a predefinedspacing distance provides a highly adaptable exterior sidewall for theshed 104, so that each exterior sidewall can be adapted to allow thetransmission of light, serve as an opaque wall, or even provide anintegrated connection of the interior space of the shed 104 to otherstructures, such as an expansion module 106. The structure of the shed104 also enables the two long exterior sidewalls to be absent—structuralreinforcements which are conventionally needed to provide strength inseismic or storm locations—consequently enabling the shed 104 to have avariety of different external wall configurations.

The expansion module 106 comprises a steel frame designed to be attachedto an open sidewall or end wall of a shed 104 to expand the usableenclosed space provided by the shed 104. For example, the expansionmodule 106 can comprise major columns 114 that form the corners of itsstructural frame, at least two of the columns being external to the shed104 and two other columns being integrated into a sidewall of the shed104. The expansion module 106 also has a sidewall with minor columns 116that can be spaced apart as described in the minor columns of the shed104 to allow spaces for light-permeable panes 188, doors, or otherstructures. A single wide-flange beam 126 bolted to a concrete gradebeam 124 can be used to support the outside sidewall of the expansionmodule 106. The expansion modules shown in FIG. 7 extend outwardperpendicularly from the shed; however, alternate arrangements arepossible, such as wedge-shaped side expansion modules, as shown in FIG.8.

The ceiling or roof plane of the modular building 100 can have variableheights and provide optional clerestory natural lighting. As a result,the modular building 100 can be tailored to a wide range of interiorenvironments while still providing a quick-to-deploy modular buildingthat is safe and long-lasting. For example, the shed 104 can comprise aroof 26 comprising a tilted support structure 122 that can be equippedwith clerestory windows along the triangular gap between the roof planeand the shed sidewall, as shown in FIGS. 6-8. The tilted supportstructure 122 has a plurality of vertical and diagonal struts that allowfor mounting of light-permeable panes in a clerestory configuration. Inone embodiment, the tilted roof support is mounted to the major columns114 of the shed 104 with hinges that allow for the tilted roof supportto be folded down to lie flat against the roof of the shed. The hingedtilted roof support allows for the roof of the modular building to belowered into a horizontal position during periods of high windconditions, which might occur during transportation of the shed 104 bytruck to the building site.

The roof structure comprises trusses 110 that rest on and are anchoredto the steel frame of the underlying shed 104 or the frame of theexpansion module 106. The trusses 110 can be steel or aluminum beams oreven composite support beams. The trusses are equipped with attachmentsurfaces 112 for fastening of roof joists 20, which span the lengthbetween trusses 110, as shown schematically in FIG. 5. The truss andjoist ceiling structure can provide support for a closed roof 202 and iseven suitable to provide a high-strength structure for situations suchas storm or high snow environments.

The ceiling 220 of the expansion module 106 can be an open ceiling or anenclosed ceiling formed by ceiling joists 20. The ceiling joists 20 arespaced apart a set distance of 4 feet, for example, and linked at theirends to the ceiling beams which are connected to one another and themajor and minor columns 114, 116. The structure provides a rigidframework which also allows easy expansion of the interior spaceprovided by the shed 104 while providing good structural strength.

Each of the sled 102, shed 104, and expansion modules 106 comprise astructural frame of modular building components, and they aretransported onto a building site with essentially all labor-intensiveand inspection-intensive work—such as welding, drilling andcutting—already completed. This allows a modular building 100 composedof the sled 102, shed 104, and optional expansion modules 106 to bequickly assembled on the site to provide a fully integrated housingstructure. The pre-manufactured structural components comprise a “kit ofparts” that only need to be joined or partially assembled withoutextensive onsite alterations to provide a high performance structurewith an adaptable interior configuration. The structures also reducerisks associated with improper assembly by requiring only minimal skilllevels for assembly and equipment usage. The assembled modular building100 can also withstand the vertical and lateral forces generated inearthquakes and storms. Further, the structures also reduce or eliminateonsite construction waste as leftover materials remain at the factoryfor recycling.

An exemplary embodiment of a modular building 100 is shown in FIG. 8;however, many other configurations are possible and can be preferred forany specific application, as would be apparent to one skilled in theart. In the embodiment of FIG. 8, the modular building 100 comprises astructure that includes a supporting sled 102, a shed 104, and twoexpansion modules 106. The sled 102 serves as a support and base for theshed 104 and can also be used to provide preassembled electricalconnections for electrical services and mechanical services, such asventilation, heating, cooling and water plumbing. The shed 104 providesan enclosed housing structure that rests on the sled 102 which serves asthe interior space of the modular building 100. The expansion modules106 can be used to expand the interior space of the modular building 100to provide extra space and to contain facilities such as restrooms,electrical power equipment or other building service equipment. In thediagram shown, the sled 102, shed 104, and expansion modules 106 haverectangular structures; however, it should be understood that othershapes and structures—for example, cylindrical or sphericalstructures—can also be used as would be apparent to those of ordinaryskill in the art. Thus, the scope of the invention should not be limitedto the illustrative embodiments described herein.

The modular building 100 can be customized to include additionalcomponents. For example, a handicapped access ramp 135 comprising arigid tilted surface 137 and handrails 138 can be provided at anentrance to the shed 104. The access ramp 134 can be configured to allowpassage of wheeled devices, such as wheelchairs and strollers, fromground level outside of the modular building 100 to the interior of theshed 104. A sun shade structure such as awning 142 can be provided tofilter or even block direct sunlight to some or all of the side panelsof the modular building 100. Solar panels 140 can be mounted on or evenintegrated into the roof structure or can be supported on peripheralstructures such as awning 142. Finally, a green roofing material 144capable of filtering pollutants from the surrounding air can be providedfor example, a layer of plants.

While illustrative embodiments of roof joist 20 are described in thepresent application, it should be understood that other embodiments arealso possible. For example, the roof joist 20 can have other shapes andstructures and can be made from other materials, as would be apparent tothose of ordinary skill in the art. Thus, the scope of the claims shouldnot be limited to the illustrative embodiments described herein.

1. A roof joist for a roof section of a modular building, the modularbuilding having an interior ceiling with a length, and the roof joistcomprising: (a) an upper chord comprising a length sufficiently long toextend substantially across the entire length of the interior ceiling ofthe roof section of the modular building; (b) a central chord joined tothe upper chord; and (c) a lower chord joined to the central chord, thelower chord comprising: (i) a top chord segment; (ii) first and secondsidewall chord segments that extend downwardly from the top chordsegment and oppose one another; and (iii) first and second outer flangesthat extend outwardly from the first and second sidewall chord segments,respectively, the flanges being capable of supporting the interiorceiling.
 2. A roof joist according to claim 1 wherein the upper chordcomprises a longitudinal and planar beam.
 3. A roof joist according toclaim 2 wherein the central chord comprises a flat beam that isperpendicular to the longitudinal and planar beam of the upper chord. 4.A roof joist according to claim 2 wherein central chord comprises twoopposing sidewall members that are parallel to one another.
 5. A roofjoist according to claim 1 wherein the upper chord comprises a firstlongitudinal hollow channel having a first enclosed volume.
 6. A roofjoist according to claim 5 wherein the central chord comprises twoopposing sidewall members that are parallel to one another and define asecond longitudinal hollow channel having a second enclosed volume, andwherein the second enclosed volume is sized larger than the firstenclosed volume.
 7. A roof joist according to claim 6 wherein the firstand second enclosed volumes each comprise a rectangular cross-section.8. A roof joist according to claim 1 further comprising first and secondinner flanges that extend inwardly from the first and second sidewallchord segments, respectively.
 9. A roof joist according to claim 8wherein a length of each of the first and second inner flanges of thelower chord is smaller than a length of an outer flange.
 10. A roofjoist according to claim 9 wherein each outer flange is sized from about2 to about 4 cm.
 11. A roof joist according to claim 9 wherein eachinner flange is sized from about 1 to about 3 cm.
 12. A roof joistaccording to claim 8 wherein each inner flange comprises an inner ridge.13. A modular building comprising a roof section defined by a pluralityof the roof joists of claim 1, a ceiling supported by the roof joists,sidewalls, and a support sled.
 14. A method of forming a roof joist fora roof section of a modular building having an interior ceiling with alength, the method comprising: (a) extruding a material to form anextrusion preform comprising an upper chord, a central chord joined tothe upper chord, and a lower chord joined to the central chord, thelower chord comprising: (i) a top chord segment; (ii) first and secondsidewall chord segments that extend downwardly from the top chordsegment and oppose one another; and (iii) first and second outer flangesthat extend outwardly from the first and second sidewall chord segments,respectively, the flanges being capable of supporting the interiorceiling; and (b) cutting the extrusion preform when the lengths of theupper, central and lower chords are each sufficiently long to extendsubstantially across the entire length of the interior ceiling of theroof section of the modular building.
 15. A method according to claim 14wherein the material comprises a metal.
 16. A method according to claim15 wherein the metal comprises steel, aluminum, iron, tin, or alloysthereof.
 17. A method according to claim 14 wherein the materialcomprises a polymer or composite material.
 18. A method according toclaim 14 wherein the material comprises a reinforced composite material.